The present invention relates to an image reading apparatus such as a copier, a facsimile machine, or a scanner which optically reads an image from a document, and in particular, to a technique for preventing dust such as paper dust from entering the interior of the apparatus through the periphery of platen glass.
In general, an image reading apparatus of this kind is commonly used in various optical machines such as an apparatus optically reading an image from a document sheet on a platen using a photoelectric conversion element. As the platen, a document fixing platen and a document traveling platen are known; a document sheet is set to remain stationary on the document fixing platen, and the document traveling platen transfers the document sheet at a predetermined speed.
For example, Japanese Patent Laid-Open No. 2002-354191 discloses an apparatus including both a document traveling platen above which a document feeding device (unit) is located to automatically feed document sheets and a document fixing platen provided with a platen cover that covers the document.
In such an apparatus, the document traveling platen requires a guide mechanism that scoops up the document sheet moving at the predetermined speed, from the platen. In general, the guide mechanism is configured such that a member surface of the guide mechanism to which the platen is fixed is composed of a guide surface so as to scoop up the document sheet from the platen (this member is hereinafter referred to as a “guide member”). The guide member forms a step that is slightly lower than the platen surface so as to avoid unwanted force to the scooped-up document sheet, for example, impact or ruck for the document sheet. Thus, as is known, dust such as paper dust may disadvantageously enter the interior through an abutting portion between the guide member and an end surface of the platen and adhere to an image reading mechanism (a mirror, a lens, or the like).
To solve this problem, for example, Japanese Patent Laid-Open No. 2002-354191 proposes a sealing mechanism in which a thin sheet such as a polyethylene film is laid so that the dust is collected on a surface of the film in order to prevent paper dust from entering the apparatus through the gap between a side end surface of the platen and the guide member.
Japanese Patent Laid-Open No. 2002-165059 proposes a sealing structure in which the guide member has a dust collecting space in which dust is collected and in which the area between the space and a bottom surface (an inner side surface of the apparatus) of the platen is filled with a film member.
Japanese Patent No. 3016306 proposes a sealing structure in which a shield member is interposed between the side end surface of the platen and the guide member.
The unwanted entry of dust into the apparatus through the document traveling platen is caused by splash of paper dust or toner from a document traveling on the platen and a failure to rigidly bond the platen and guide member together because of the need for occasional replacement of the platen due to damage to the platen surface, for example, a flaw on the platen surface, caused by the traveling document.
As described above, when the platen on which the document sheet travels is integrally coupled to the guide member scooping up the document sheet from the platen, a step needs to be formed between the platen and the guide member so as to allow the document sheet to be smoothly conveyed. Furthermore, for maintenance, the platen needs to be removed to open the interior of the apparatus. Thus, dust such as paper dust may disadvantageously accumulate in the area between the platen and the guide member and further enter the interior of the apparatus.
To prevent the possible entry of dust, the shield structures proposed in the above-described patent documents have been adopted. For example, in the apparatus disclosed in Japanese Patent Laid-Open No. 2002-354191, the elastic film material is laid between the bottom surface of the platen and the guide member, which supports the bottom surface, to prevent dust from entering the interior. Similarly, in the apparatus disclosed in Japanese Patent No. 3016306, the shield member such as a sponge is placed between the end surface of the platen and the guide member to prevent dust from entering the interior.
The structure in which the shield member is interposed between the platen and the guide member allows dust such as paper dust to be collected in the step portion between the platen and the guide member. The dust collected at an edge of the platen may disadvantageously adhere to the platen surface when the platen glass becomes hot. That is, the temperature of the platen glass is increased by heat from an exposure lamp, and the heat further causes the dust such as toner ink to be deposited on the platen surface. Furthermore, in an apparatus configuration in which a document conveying unit located above the platen is opened and closed, a heavy mechanical impact acts on the platen every time the document conveying unit is opened or closed. Vibration and wind pressure caused by the opening or closing of the document conveying unit may create a gap in the shield member. As a result, dust collected on the step portion may enter the interior of the apparatus through the gap.
Thus, a structure has been proposed in which a dust collecting space is formed in the guide member to collect the dust in the space as disclosed in Japanese Patent Laid-Open No. 2002-165059. However, the structure proposed in Japanese Patent Laid-Open No. 2002-165059 simply has the space (dust collecting chamber) in which dust entering through the end surface of the platen is collected. Thus, the dust collected in the space may disadvantageously enter the interior of the apparatus. That is, in the structure of Japanese Patent Laid-Open No. 2002-165059, the dust collecting chamber is blocked with the film member (sealing member) provided on the platen. Thus, when vibration or wind pressure acts on the platen as described above, dust may disadvantageously leak into the interior of the apparatus through the sealing portion.
The present inventor focuses on the fact that the operation of opening or closing the document conveying unit applies shocking vibration and wind pressure to the platen glass and cause dust such as paper dust to enter the interior of the apparatus. The present inventor has thus conceived the idea that by forming a dust collecting space (dust collecting pocket) in the guide member and regulating the motion of dust collected in the pocket when the dust falls under the effect of vibration or wind pressure, the disadvantageous possible entry of dust into the interior of the apparatus can be prevented.
A main object of the present invention is to provide an image reading apparatus that prevents dust such as paper dust from entering the interior of the apparatus when the platen is coupled to the guide member, which scoops up the traveling document from the platen.
Further objects and advantages of the invention will be apparent from the following description of the invention.